Turing, born in 1912, is also famous for creating code-breaking machines during World War Two at Bletchley Park. The British Bombe machine broke German Engima codes, a major advantage to Allied forces during the war. After the war, he created what is now known as the Turing Test, a method of establishing whether a machine can “think.” If a human can’t tell the difference between a machine’s response and that of another human being, then the machine is judged to exhibit intelligent behavior.

“As the father of computer science and artificial intelligence, as well as war hero, Alan Turing’s contributions were far ranging and path breaking,” Mark Carney, governor of the Bank of England, said in published remarks today. “Turing is a giant on whose shoulders so many now stand.”

Bank of England

Concept design.

While Turing’s contribution to modern technology is now revered, he suffered during his lifetime as a consequence of his homosexuality, which was a crime at the time. Turing was convicted in 1952 of gross indecency for his relationship with a man. To avoid a prison sentence, he was chemically castrated. He died two year later, at the age of 41, which an inquiry ruled as suicide. Turing was posthumously pardoned by the Queen in 2013. In 2017, the Alan Turing Law was passed, which posthumously pardoned men cautioned or convicted under historical legislation that outlawed homosexual acts.

The design on the reverse of the banknote will feature:

A photo of Turing taken in 1951.

A table and mathematical formulae from Turing’s 1936 paper “On Computable Numbers, with an application to the Entscheidungsproblem” (“decision problem”). The paper is considered foundational for computer science and included a description of the device now called the Turing Machine.

The trial model of Turing’s Automatic Computing Engine machine.

Technical drawings for the British Bombe, the machine specified by Turing and one of the primary tools used to break Enigma-enciphered messages during WWII.

A quote by Turing, given in an interview to The Times newspaper in 1949: “This is only a foretaste of what is to come, and only the shadow of what is going to be.”

Turing’s signature from the visitor’s book at Bletchley Park in 1947, where he worked during WWII.

The new £50 note is expected to enter circulation by the end of 2021. The UK has been redesigning its banknotes as the bank upgrades them to use polymer materials. In 2016, the polymer £5 notes was put into circulation with Winston Churchill. A year later, Jane Austen followed on the £10. Artist JMW Turner will feature on the £20 when they are entered into circulation next year. There are currently more thank 3.6 billion notes in circulation worth about £70 billion. About £17 billion of this is in £50 notes.

The choice of Turing for the banknotes is also fitting as the UK seeks to become a global leader in AI, making it a focus of its industrial strategy. DeepMind, now owned by Alphabet, is arguably the most famous British AI company. AI companies in the UK raised a record £1.3 billion in capital last year.